Electron Spin Resonance Tests Research Articles

Visible-Light Photocatalytic Degradation Efficiency of Tetracycline and Rhodamine B Using a Double Z-Scheme Heterojunction Catalyst of UiO-66-NH2/BiOCl/Bi2S3.

BiOCl is a promising photocatalyst, but due to its weak visible light absorption capacity and low photogenerated electron-hole pair separation rate, its practical application is limited to a certain extent. In this study, a novel double Z-scheme heterojunction UiO-66-NH2/BiOCl/Bi2S3 catalyst was constructed to broaden the visible light response range and promote high photogenerated hole-electron separation of BiOCl. Its photocatalytic performance is evaluated by dissociating tetracycline (TC) and rhodamine B (RhB) in visible light. The optimal proportion of UiO-66-NH2/BiOCl/Bi2S3 hybrids exhibits the best degradation efficiency of visible light illumination (∼93% in 120 min for TC and ∼98% in 60 min for RhB). The synergistic effect of a large visible light response range and the Z-scheme charge transfer mechanism ensure the excellent visible photocatalytic activity of UiO-66-NH2/BiOCl/Bi2S3. It is proven that h+ and •O2- are the main active substances in the photocatalysis process by active substance capture experiments and electron spin resonance tests. The intermediates and degradation processes are analyzed by high-performance liquid chromatography-mass spectrometry. This study proves that the new UiO-66-NH2/BiOCl/Bi2S3 photocatalyst has great application potential in the field of water pollution degradation and will provide a new idea for the optimization of BiOCl.

Roles of soil minerals in the degradation of chlorpyrifos and its intermediate by microwave activated peroxymonosulfate

Soil mineral is one of the important factors that affecting oxidant decomposition and pollutants degradation in soil remediation. In this study, the effects of iron minerals, manganese minerals and clay minerals on the degradation of chlorpyrifos (CPF) and its intermediate product 3,5,6-trichloro-2-pyridinol (TCP) by microwave (MW) activated peroxymonosulfate (PMS) were investigated. As a result, the addition of minerals had slight inhibitory effect on the degradation efficiency of CPF by MW/PMS, but the degradation efficiency of TCP was improved by the addition of some specific minerals, including ferrihydrite, birnessite, and random symbiotic mineral of pyrolusite and ramsdellite (Pyr-Ram). The stronger MW absorption ability of minerals is beneficial for PMS decomposition, but the MW absorption ability of minerals cannot be fully utilized because of the weaker MW radiation intensity under constant temperature conditions. Through electron spin resonance test, quenching experiment and electrochemical experiment, electron transfer, SO4− and OH, SO4− dominated TCP degradation by MW/PMS with the addition of birnessite, Pyr-Ram and ferrihydrite, respectively. Besides, the adsorption effect of ferrihydrite also enhanced the removal of TCP. The redox of Mn (III)/Mn (IV) or Fe (II)/Fe (III) in manganese/iron minerals participated in the generation of reactive species. In addition, the addition of minerals not only increased the variety of alkyl hydroxylation products of CPF, causing different degradation pathways from CPF to TCP, but also further degraded TCP to dechlorination or hydroxylation products. This study demonstrated the synergistic effect of minerals and MW for PMS activation, provided new insights for the effects of soil properties on soil remediation by MW activated PMS technology.

Chemically bonded CdBiO2Br/BiOI heterojunction with strong interfacial electric field for enhanced photocatalysis

Semiconductor-based photocatalysis shows a large potential for contaminant purification, however, a single semiconductor photocatalyst suffers from low utilization efficiency of photogenerated carriers, leading to inferior photocatalytic activity. Herein, CdBiO2Br@BiOI (CBOB@BiOI) heterojunction with a close interface interaction is prepared by a facile precipitation method at the ambient atmosphere. X-ray photoelectron spectroscopy and Density Functional Theory calculations on work function consistently disclose that the formation of CdBiI bonds at the interface induces the electron migration from BiOI to CdBiO2Br, which allows CBOB@BiOI heterojunction to have a strong interfacial electric field (IEF) for efficiently separating photocharges. In-situ Kelvin-probe Force Microscopy measurement demonstrates that CBOB@BiOI heterojunction shows a larger surface potential than CdBiO2Br and BiOI in dark and a potential decrease under illumination, which can be ascribed to the photoinduced electron migration within heterojunction driven by the IEF. Thus, the CBOB@BiOI heterojunction shows a much more efficient photocatalytic activity for the breakdown of tetracycline hydrochloride (TC), which is 2.44 and 3.99 times higher than CdBiO2Br and BiOI, respectively. Electron Paramagnetic Resonance test also confirms that the CBOB@BiOI heterojunction produces much more superoxide radicals and holes as reactive species than CdBiO2Br and BiOI. Furthermore, the latent degradation pathways of TC are investigated by Liquid Chromatograph Mass Spectrometer. This work may provide new ideas for constructing intimately bonded heterojunction photocatalysts with a strong IEF for efficient photocatalytic activity.

Enhanced inactivation of Escherichia coli through hydrogen peroxide decomposition assisted by nanoscale cupric oxide-decorated activated carbon

In this study, nanoscale cupric oxide-decorated activated carbon (nCuO@AC) was synthesized by impregnation-calcination and employed to assist the decomposition of H2O2 for effective sterilization with Escherichia coli as target bacteria. Characteristic technologies demonstrated that copper oxide particles of 50–100 nm were uniformly distributed on AC surface. Owing to electron transfer from hydroxyl and aldehyde to CuO on AC, surface-bonded Cu(II) was partially reduced to Cu(I) in the nCuO matrix. The resultant Cu(I) expedited the decomposition of H2O2 and converted it into ·OH radicals which were identified by quenching experiment and electron paramagnetic resonance test. Due to oxidation attack of generated ·OH, the nCuO@AC-H2O2 system achieved a much higher inactivation rate of 6.0 log within 30 min as compared to those of 2.1 and 1.3 log in the nCuO@AC and nCuO-H2O2 systems. It also exhibited excellent pH adaptability and high inactivation efficiency under neutral conditions. After four cycles, the nCuO@AC-H2O2 system could still inactivate 5.5 log bacteria, indicating excellent stability and reusability of nCuO@AC. Spent nCuO@AC could be regenerated by eluting surficial copper oxides with hydrochloric acid, and re-coating nCuO particles through impregnation-calcination with a regeneration rate of 96.6%. Our results demonstrated that nCuO@AC was an efficient and prospective catalyst to assist the decomposition of H2O2 for effective inactivation of bacteria in water.

Unraveling the intrinsic activity origin of sludge-derived biochar for boosted chlorination of diclofenac: Key role of persistent free radicals

Economical and eco-friendly chlorine-based advanced oxidation processes (AOPs) have been urgently demanded to enhance the green abatement of emerging micropollutants. Herein, sludge-derived biochar (SBC) was innovatively introduced to activate free available chlorine (FAC) to enhance the elimination of diclofenac (DCF) among pH 5.0–11.0. Pyrolysis of municipal sludge endowed biochar with superior structure, various chemical compositions, and electronic properties, among which carbon-centered persistent free radicals (PFRs) were verified as the dominant active sites for enhanced chlorination based on correlation analysis. Electron spin resonance and electrochemical tests firstly verified that PFRs could mediate electron transfer toward FAC and dissolved oxygen to generate multiple reactive species of •OH, ClO•, 1O2, and O2•−. Further investigation revealed that enhanced DCF chlorination relied on both radical attack by •OH, ClO•, O2•− and direct electron transfer. Meanwhile, the regeneration of PFRs mediated by FAC and electron-rich DCF greatly promoted the reusability of SBC800. SBC800/FAC system was much superior to sole chlorination in terms of toxicity reduction and anti-interference capacity. This study innovatively introduced SBC as a green and sustainable catalyst to enhance chlorination efficiency, and provided new insights into the activation potential and mechanism of PFRs for chlorination.

Electrochemical selection of ferrous phosphide (FexP) as efficient catalyst for wastewater treatment: Performance and mechanism

Iron phosphide (FexP) has a great potential for electrochemical catalysis attributing to its outstanding electrical conductivity and activity. In the present study, a series of FexP (FeP, Fe2P and Fe3P) were carried out as catalysts for the oxidation of phenol from wastewater by the heterogeneous EF processes. Compared with FeP and Fe2P catalysts, Fe3P has shown significant two-electron oxygen reduction activity and H2O2 selectivity (90–100 %). The degradation efficiencies of phenol in Fe3P/EF (100 %) were higher than those in Fe2P/EF (91 %) and FeP/EF (67 %) upon 60-min electrochemical oxidation under pH 7. The Fe3P-CF/EF system could broaden the range of solution pH, as well the decay kinetics of phenol was enhanced by 1.5–2.4 times and the disposal cost was reduced by 33–41 % compared with FeP/EF and Fe2P/EF. Feɑ+ in Fe3P could promote the generation of •OH via accelerating Fe(II)/Fe(III) cycle and accelerating the transfer rate of electrons between Fe3P and H2O2. It was proved that •OH played a dominant role in removing phenol with the electron spin resonance (ESR) tests and trapping experiments. This work selected the most effective FexP catalyst in heterogeneous EF process and would bring new insights for organics removal from wastewater via H2O2 activation.

Modulating band structure of g-C3N4 by doping oxygen to transform FeCo2O4/g-C3N4 heterojunction from type-II to S-scheme for enhancing photo-Fenton-like reaction

Constructing S-scheme heterojunctions is a highly prevalent approach in enhancing the activation efficiency of peroxymonosulfate (PMS). However, the two semiconductors that have the potential to form S-scheme heterojunction (such as FeCo2O4 and carbon nitride) typically tend to form type-II heterojunction. In this study, through oxalic acid assisted oxygen atom doping in carbon nitride, followed by the utilization of oxygen-doped carbon nitride (O-CN) as precursors in combination with cobalt chloride and iron chloride, the final synthesis of a novel composite catalyst is achieved. The introduction of oxygen atoms into the graphite carbon nitride can lead to an overall reduction in the band structure, facilitating the controlled transformation of a type-II heterojunction to an S-scheme heterojunction. This transformation is confirmed through density functional theory (DFT) calculations and electron spin resonance (ESR) tests. In the photo-Fenton-like system, the 15 % FeCo2O4/Oxygen doped-C3N4 (FCOCN) catalyst demonstrated a remarkable degradation efficiency of 93.5 % for tetracycline hydrochloride (TCH). This efficiency surpassed that of O-CN (47.8 %) and FeCo2O4 (60.3 %). Furthermore, the degradation efficiency of the 15 % FCOCN catalyst was significantly higher than that of photocatalysis (2.04 times greater) and Fenton-like treatment (1.11 times greater). Remarkably, within a short period of 14 min, the emerging contaminants, including sulfamethoxazole (SMX), bisphenol A (BPA), and carbamazepine (CBZ), were completely degraded. Atrazine (ATZ) showed a remarkable degradation rate of 77.1 %. This study offers valuable insights into the construction of S-scheme heterojunction through the manipulation of band structure in type-II heterojunction by oxygen doping.

Fabrication of porous biochar supported Bi2MoO6 photocatalyst for efficient degradation of ciprofloxacin in seawater under visible light irradiation: Mechanistic investigation and intermediates analysis

Efficient separation of photocarriers is a critical approach for advancing high-performance photocatalyst systems to effectively remove environmental contaminants. In this investigation, a hydrothermal technique was employed to synthesize composites of Bi2MoO6 and porous biochar derived from banana peels (BPB). The samples underwent various characterization methods to assess their composition, morphology, and photoelectrochemical properties. The BPB/Bi2MoO6 composite exhibited a synergistic adsorption and photocatalytic impact in eliminating the antibiotic ciprofloxacin (CIP) from pure water and seawater. The optimized BPB/Bi2MoO6 sample displayed a significant degradation efficiency of 98.7 % for CIP after 90 min of visible-light exposure in pure water. In artificial seawater, the degradation efficiency for CIP remained high at 93.6 %, which was 12.2 times greater than that of pure Bi2MoO6. The study also explored the impact of various factors such as catalyst dosage, solution pH, and pollutant concentration on the photocatalytic performance of BPB/Bi2MoO6. Moreover, the catalyst exhibited enhanced efficiency in the adsorption-photocatalytic degradation of CIP within a continuous flow reaction system. The enhanced photocatalytic performance was attributed to the composite's exceptional adsorption capacity, enhanced response to visible light, and efficient separation of photoinduced electron-hole pairs. Furthermore, the BPB/Bi2MoO6 photocatalyst displayed good stability and recyclability over five consecutive photodegradation cycles. Radical trapping and electron spin resonance (ESR) experiments verified that the degradation of CIP was mainly driven by •OH and h+ radicals. A thorough investigation employing density functional theory (DFT), radical trapping and ESR tests, and liquid chromatography mass spectrometry (LC-MS) was conducted to elucidate the degradation mechanism and pathways. Furthermore, toxicity assessment software was utilized to illustrate the progressive reduction in toxicity of the intermediate products. In conclusion, this study provides valuable insights into the role of biochar in enhancing the photocatalytic degradation of pollutants and offers guidance for the future development of environmentally friendly photocatalysts.

Salt assistant bimetallic sludge-derived porous carbon for efficient peroxymonosulfate activation

The development of cost-effective, environmentally benign, and high-performance peroxymonosulfate (PMS) activation towards wastewater treatment is still considered a challenge. In this work, the sludge-derived porous carbon loaded with bimetal oxides (DSC-FeMn) was fabricated by molten salt assistant strategy using the combination of zinc chloride, metal ions and Fe containing sludge. The obtained DSC-FeMn exhibited high catalytic activity for nearly 100 % 4-chlorophenol (4-CP) removal within 30 min with the k of 0.304 min−1, which was 1.07 and 11.94 times that of the single Fe and Mn-sludge-derived carbon (DSC-Fe, DSC-Mn), respectively. Quenching experiments, electron paramagnetic resonance tests (EPR), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR) and electrochemical experiments proved that the radical pathway, dominated by OH and SO4−, led to the excellent degradation performance of DSC-FeMn, which was attributed to the redox cycling between Fe and Mn. This study provides a new idea for sludge resource utilization, and it deepens the understanding of the mechanism of PMS activation by the synergistic interaction between bimetal.

La0·8Mn0·2FeO3 impregnated ceramic membrane for membrane fouling elimination via peroxymonosulfate activation

To endow SiC ceramic membranes a catalytic self-cleaning capability, a pore-functionalized SiC ceramic membrane with impregnated a perovskite-type catalyst La0·8Mn0·2FeO3 was fabricated by a urea-assisted one-step combustion method. Diffraction of X-ray (XRD), canning electronic microscopy (SEM) with an energy dispersion X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were employed to investigate the effects of the impregnating of La0·8Mn0·2FeO3 on SiC membrane pore-structure (La0·8Mn0·2FeO3-CM). The catalytic self-cleaning performance of the as-prepared membranes was assessed through peroxymonosulfate (PMS) activation under a cross-flow filtration mode. Results indicate that La0·8Mn0·2FeO3 has been successfully impregnated into the macropores of SiC membranes without pore blocking, and 92.4 % of the flux recovery rate (FRR) was achieved when the PMS concentration was 70 mM and catalytic flushing time was 45 min. Therefore, the La0·8Mn0·2FeO3 impregnated SiC membrane exhibited excellent catalytic self-cleaning property, which can effectively avoid the environmental pollution and the deterioration of membrane materials caused by chemical cleaning for membrane fouling. In addition, the radical quenching experiment and electron spin resonance (EPR) tests were conducted in the catalytic self-cleaning process, and the results suggested that the hydroxyl radical (⋅OH) and sulfate radical (SO4•‾) are simultaneously captured and ⋅OH is the dominant active species. This study embarks on a novel and environmental friendly membrane cleaning approach for irreversible fouling eliminates in diverse membrane separation applications.

Insights into nitrogen-doped BiOBr with oxygen vacancy and carbon quantum dots photocatalysts for the degradation of sulfonamide antibiotics: Actions to promote exciton dissociation and carrier migration

The strong excitonic effect significantly influences the efficiency of electron-hole pair generation. Therefore, promoting the dissociation of excitons into free charge carriers has drawn much attention. In this study, nitrogen (N)-doped BiOBr photocatalyst (BOBNC) modified with carbon quantum dots (CQDs) was synthesized via a solvothermal method. We demonstrated through photoluminescence and photoelectrochemical techniques the synergistic effect of oxygen vacancies and CQDs, facilitating exciton dissociation and charge carrier migration, consequently significantly enhancing the electron density in the material. Compared to pure BiOBr, degradation experiments revealed that the optimized doping ratio of 0.5BOBNC with CQDs increased the rate constant for sulfamethoxazole (SIZ) by 19.89 times. Furthermore, based on quenching experiments, electron spin resonance (ESR) tests, and DFT calculations, h+, O2•− and 1O2 were identified as the primary reactive species for SIZ degradation, and a photocatalytic mechanism was proposed. Additionally, the influence of various environmental factors on the photocatalytic system was investigated. In conclusion, this work not only contributes to a profound understanding of BiOBr exciton dissociation but also presents a promising photocatalytic technique for the remediation of diverse water environments.

Copper Phenylacetylide and TiO2 Modification for an Efficient Visible-Light-Driven Oxidative Coupling of Amines.

The selective oxidation of amines to imines under mild conditions has attracted much attention. Our study reveals that copper phenylacetylide (PhC2Cu) could serve as an efficient photocatalyst for imine synthesis under visible-light irradiation (>400 nm). Utilizing benzylamine as a model reactant, PhC2Cu achieves an imine yield of 50.4%, which is 5 times higher than that of P25 under the same conditions and comparable to the yield obtained by the 3 wt % Au/P25 photocatalyst (55.4%). Further loading 3.9 nm TiO2 onto PhC2Cu through tetrabutyl titanate hydrolysis increases the imine yield to 84.7%, with a Ti:Cu atomic ratio of 3.65%. Control experiments, photoluminescence (PL) spectra, optical pump terahertz probe (OPTP) spectra, and electron spin resonance (ESR) tests confirm that the optimized TiO2 modification promotes the separation of excited carriers and electron transfer in PhC2Cu and facilitates the activation of surface oxygen, thereby enhancing the formation of superoxide radicals, a key active oxygen species in the reaction system. This work presents a promising strategy for efficient imine synthesis via amine coupling and expands the application field of PhC2Cu-based photocatalysts.

Sn/Sb–assisted alum sludge electrodes for eliminating hydrophilic organic pollutants in self-produced H2O2 electro-Fenton system: Insights into the co-oxidation mediated by 1O2 and •OH(ads)

Few reports have focused on using particle electrodes with polar adsorbent properties in heterogeneous electro-Fenton (EF) system to improve the degradation of hydrophilic organic pollutants (HLOPs). In this study, a hydrophilic electrode Sn–Sb/AS was prepared by supporting metals Sn and Sb on alum sludge (AS), which can effectively degrade 91.68%, 92.54%, 89.62%, and 96.24% of the four types of HLOPs, chlorpyrifos (CPF), atrazine (ATZ), diuron (DIU), and glyphosate (PMG), respectively, within 40 min. The mineralization rates were 82.37%, 78.93%, 73.98%, and 85.65% for CPF, ATZ, DIU, and PMG, respectively. Based on the analysis of Electron Paramagnetic Resonance test, quenching test, and identified anthracene endoperoxide, the degradation at the cathode was attributed to non-radical oxidation via interaction with 1O2. In contrast, the anodic oxidation occurred via direct electron transfer at the anode and/or oxidation via interaction with adsorbed •OH (•OHads) around the particle electrodes. Furthermore, the reaction sites were calculated by Density functional theory (DFT) and Fukui function, corresponding to the electrophilic attack (fA-) of 1O2 and anodic direct oxidation, besides, the radical attack (fA0) of •OH(ads). Herein, this study proposes a targeted elimination strategy for HLOPs in wastewater treatment using particle electrodes with polar adsorbent properties in EF system.

Construction of Zn0.5Cd0.5S/Bi4O5Br2 Heterojunction for Enhanced Photocatalytic Degradation of Tetracycline Hydrochloride

The development of efficient catalysts with visible light response for the removal of pollutants in an aqueous environment has been a hotspot in the field of photocatalysis research. A Zn0.5Cd0.5S (ZCS) nanoparticle/Bi4O5Br2 ultra-thin nanosheet heterojunction was constructed by ultrasound-assisted solvothermal method. The morphology, structure, and optoelectronic properties of the composite were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. Under simulated visible light illumination, the photocatalytic performance was evaluated through degradation of tetracycline hydrochloride. Results show that the degradation effect by the optimum ZCS/Bi4O5Br2 catalyst is superior to pure materials with the kinetic constant that is 1.7 and 9.6 times higher than those of Bi4O5Br2 and ZCS, and also has better stability and reusability. Trapping experiments and electron paramagnetic resonance tests find that free radicals in the photocatalytic system are superoxide radicals and holes. This work provides a referable idea for the development of more efficient and recyclable photocatalysts.

Incorporation of Shewanella oneidensis MR-1 and goethite stimulates anaerobic Sb(III) oxidation by the generation of labile Fe(III) intermediate

Dissimilatory iron-reducing bacteria (DIRB) affect the geochemical cycling of redox-sensitive pollutants in anaerobic environments by controlling the transformation of Fe morphology. The anaerobic oxidation of antimonite (Sb(III)) driven by DIRB and Fe(III) oxyhydroxides interactions has been previously reported. However, the oxidative species and mechanisms involved remain unclear. In this study, both biotic phenomenon and abiotic verification experiments were conducted to explore the formed oxidative intermediates and related processes that lead to anaerobic Sb(III) oxidation accompanied during dissimilatory iron reduction. Sb(V) up to 2.59 μmol L−1 combined with total Fe(II) increased to 188.79 μmol L−1 when both Shewanella oneidensis MR-1 and goethite were present. In contrast, no Sb(III) oxidation or Fe(III) reduction occurred in the presence of MR-1 or goethite alone. Negative open circuit potential (OCP) shifts further demonstrated the generation of interfacial electron transfer (ET) between biogenic Fe(II) and goethite. Based on spectrophotometry, electron spin resonance (ESR) test and quenching experiments, the active ET production labile Fe(III) was confirmed to oxidize 94.12% of the Sb(III), while the contribution of other radicals was elucidated. Accordingly, we proposed that labile Fe(III) was the main oxidative species during anaerobic Sb(III) oxidation in the presence of DIRB and that the toxicity of antimony (Sb) in the environment was reduced. Considering the prevalence of DIRB and Fe(III) oxyhydroxides in natural environments, our findings provide a new perspective on the transformation of redox sensitive substances and build an eco-friendly bioremediation strategy for treating toxic metalloid pollution.

Construction of an all-organic S-scheme heterostructure based on PEDOT immobilized g-C3N4 nanosheets by electrostatic self-assembly with enhanced visible-light photocatalytic hydrogen production

Inspired by photosynthesis in nature, exploring all-organic S-scheme heterojunction photocatalysts for efficient H2 production is of great significance in addressing energy shortage issues. In this paper, poly(3,4-ethylenedioxythiophene) (PEDOT) immobilized g-C3N4(CN) nanosheets were constructed by an electrostatic self-assembly strategy to obtain an all-organic S-scheme heterojunction, significantly enhancing the visible-light photocatalytic H2 production performance of g-C3N4. The optimized 5PEDOT/CN exhibits the highest H2 production rate of 3.15 mmol g−1h−1, a 31.5-fold enhancement over pristine CN. According to the staggered energy band positions of two components and the results of electron spin resonance tests, the S-scheme heterojunction electron-transfer mechanism is confirmed, which greatly facilitates the spatial charge separation and retains the strong reducing ability of high-energy potential electrons for efficient photocatalytic H2 production. Based on the results of FT-IR spectra, XPS spectra, fluorescence spectra, hydroxyl radical tests and time-resolved photoluminescence spectra, it is confirmed that the significantly improved photocatalytic activity is mainly attributed to the enhanced charge separation by the S-scheme heterojunction and the tightly contacted interface dependent on N···S interactions in PEDOT immobilized CN nanosheet heterojunctions, along with the enhanced visible-light absorption ability. This work presents a novel approach to the design and fabrication of all-organic S-scheme heterojunction photocatalysts for solar-light-driven energy production.

Electro-controlled membrane coupling heterogeneous electro-Fenton (EM-HEF) in treating acetaminophen: performance, mechanism, DFT calculation, and application

The utilization of hybrid electro-Fenton (EF) processes has gained considerable attention, which can combine the advantages of two or more treatment methods resulting in efficient removal of refractory pollutants from water. Here, an electro-controlled membrane coupling heterogeneous EF (EM-HEF) system was constructed for the degradation of acetaminophen (APAP) in water. In the EM-HEF system, a bifunctional ACF/CC-FeOCl-Cu cathode material was synthesized to enhance the HEF reaction, while a tubular Ti microfiltration membrane was used as both cathode and membrane. Degradation experiments indicated the EM-HEF system exhibited remarkable removal efficiency (97.0 %) towards APAP within 30 min under the conditions of flow rate at 60 mL min−1, initial pH at 7.1, and current density at 3 mA cm−2. Notably, the cathode materials showed low metal leaching rate and high APAP removal rate in the 10 cyclic experiments. The common inorganic anions (Cl−, HCO3−, HPO42−, and NO3−) did not inhibit the removal of APAP significantly, whereas humic acid exhibited a more pronounced inhibitory effect only at concentrations exceeding 10 mg L−1. Quenching experiments and electron spin resonance (ESR) tests confirmed the pivotal role of hydroxyl radicals in the decomposition of APAP. Combining density functional theory (DFT) and LC-MS results, three pathways were proposed. The overall toxicity of intermediates was relieved during EM-HEF degradation of APAP. Furthermore, it also achieved good performance in the treatment of landfill leachate, with increasing BOD5/COD ratio from 0.11 to 0.34. This work provides an efficient strategy for the removal of refractory pollutants in water.

Hydroxylamine enhanced Fe3O4/H2O2 system for removing tartrazine

In recent years, dye wastewater caused serious effects on environmental ecology and human health. Thus, in the present study, hydroxylamine (HA) was used to improve the Fe3O4/H2O2 process for removing the typical dye pollutant (tartrazine). Only 2.8% tartrazine could be removed in Fe3O4/H2O2 system within 60 min at the reaction of 1 g/L Fe3O4, 1 mM H2O2, and pH 4 while 97.5% tartrazine could be removed within 20 min after adding 1 mM HA into the Fe3O4/H2O2 system. Compared with Fe3O4/H2O2 system, the removal rate for removing tartrazine in Fe3O4-HA/H2O2 system could enhance more than 100 times. Electron paramagnetic resonance tests (EPR), radical quenching experiments and quantitative determination demonstrated that •OH was the major reactive species for removing tartrazine in Fe3O4-HA/H2O2 system and •OH produced concentration in Fe3O4-HA/H2O2 system was also much higher than that in Fe3O4/H2O2 system. The key factors affecting tartrazine removal in Fe3O4-HA/H2O2 system were also conducted. The optimal HA dosage, Fe3O4 dosage, and H2O2 dosage was 1 mM, 1 g/L and 1 mM. The optimal initial pH in Fe3O4-HA/H2O2 system was 3, but compared with Fe3O4/H2O2 system, the tatrazine removal efficiency could significantly improve under any initial pH condition. Fe3O4-HA/H2O2 process had strong adaptability to inorganic ions and good applicability to different pollutants. Fe3O4-HA/H2O2 process also exhibited good recycle ability for tartrazine removal. Overall, Fe3O4-HA/H2O2 process is an effective and good practical applicability approach for dye wastewater treatment.

Highly efficient visible-light driven dye degradation via 0D BiVO4 nanoparticles/2D BiOCl nanosheets p-n heterojunctions

The construction of hybrid heterojunction photocatalysts is an effective strategy to improve the utilization of photogenerated carriers and photocatalytic activity. To enhance the separation distance of photogenerated carriers and accelerate the effective separation at the heterojunction of the interface, a unique 0D-2D hierarchical nanostructured p-n heterojunction was successfully fabricated in this work. BiOCl (BOC) nanosheets (p-type) were in situ grown on BiVO4 (BVO) nanoparticles (n-type) using the microemulsion-calcination method for highly efficient visible-light-driven organic dye degradation. Compared with pure BVO (the degradation rate of rhodamine B (RhB): about 32.0% in 55 min, the mineralization rate: 24.9% in 120 min), the RhB degradation rate can reach about 99.5% in 55 min and the mineralization rate of 62.1% in 120 min by utilizing BVO/25%BOC heterojunction photocatalyst under visible light irradiation. Various characterizations demonstrate that the formation of BVO/BOC p-n heterojunction greatly facilitates photogenerated carriers separation efficiency. Meanwhile, the results of the scavenging experiments and electron spin resonance tests indicate that ·O2− and h+ are the prominent active species for Rh B degradation. In addition, possible degradation pathways for Rh B were proposed using LC-MS tests. This work proves that building low dimensional p-n heterojunction photocatalysts is a promising strategy for developing photocatalysts with high efficiency.

Selective oxidation of ammonia nitrogen to nitrogen gas by Fe2+/PMS/Cl−: The role of reactive chlorine species

Ammonia nitrogen (NH4+-N) can pose a threat to ecosystems and human health. Many methods have been used for the removal of NH4+-N. In particular, reactive chlorine species (RCS, including Cl·, Cl2·−, and ClO·) show superior performance for the selective oxidation of NH4+-N to nitrogen gas (N2). Herein, Fe2+/peroxymonosulfate (PMS)/Cl− process was proposed to generate RCS for the conversion of NH4+-N to N2, in which Fe2+ was used as the activator of PMS in the presence of Cl−. Fe2+, PMS, and Cl− concentrations could affect the removal of NH4+-N in Fe2+/PMS/Cl− process. Fe2+/PMS/Cl− exhibited good performance in removing NH4+-N at pH 3.5–8.0. At all investigated conditions, NH4+-N was mainly converted to N2, and N2 selectivity was more than 90 %. Under optimal conditions, 50 % of NH4+-N was removed in 5 min, and the removal efficiency reached the maximum of 96 % within 120 min with the high N2 selectivity of 100 %. The electron spin resonance tests, scavenging experiments, and probe experiments demonstrated the generation of RCS in Fe2+/PMS/Cl− reaction system. Experimental results and model analysis consistently proved that ClO· and Cl· were crucial radicals during the selective oxidation of NH4+-N, especially ClO·. Fe2+/PMS/Cl− system could remove NH4+-N and COD simultaneously in real wastewater. This study can provide an efficient strategy for the removal of NH4+-N.